The pollution of the atmosphere due to industrial waste gases is a problem of ever increasing magnitude. Specifically, the emission of SO.sub.2 in smelting and power plant stack gases is of primary concern and controls on the SO.sub.2 concentration have been set by the Federal Government. A few states (California and New Jersey) have set 2000 ppm as maximum SO.sub.2 in stack gas. New plants are warned that 500 ppm maximum is in the foreseeable future. In general, 2000 ppm is maximum allowable SO.sub.2 concentration in most states. Stack gas from smelters typically will contain 7-8 percent SO.sub.2, and from power plants about 0.4-0.6 percent SO.sub.2.
The effluent stack gas from power generation plants is fairly typical of stack gases in respect to SO.sub.2 and CO.sub.2 content. In general, the ratio between SO.sub.2 and CO.sub.2 is 1-50.
The use of alkanolamines in combination with water for the absorption of acid gases is known. Such a process is disclosed, for example, in U.S. Pat. No. 2,797,188. Furthermore, the use of mixtures of alkanolamines with other compounds is also known. Such processes are disclosed, for example, in U.S. Pat. Nos. 3,039,251 and 3,387,917.
Reactivation of spent alkanolamine absorbents employed in cyclic processes for scrubbing acid gases by contacting the alkanolamine absorbent with a strongly basic anionic exchange resin is also described in U.S. Pat. No. 2,797,188.
However, in none of these processes is revealed the step of selectively absorbing the SO.sub.2 in preference to the CO.sub.2, thereby allowing the CO.sub.2 to be vented without the need of stripping it or otherwise removing it or its corresponding alkanolamine salt from the absorbent medium.